Single tube radio receiver



g- 1937- G. JOBST ET AL 2,090,051

SINGLE TUBE RADIO RECEIVER Filed Sept. 25, 1933 INVENTOR GOA 779E)? JOBST D/ETE/(f/ AQ/A ATTORNEY Patented Aug. 17, 1937 SINGLE TUBE RADIO RECEIVER Gunther Jobst and Dietrich Prinz, Berlin, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application September 23, 1933, Serial No. 690,640 In Germany September 20, 1932 1 Claim.

The present invention discloses ways and means to build a single-stage set by means of which the loudspeaker may be used not only for the electric rendition of phonograph records, but also for 5 broadcast reception.

In order that adequate volume may be obtained with a loudspeaker it is necessary that the modulation of the plate current in the power stage should be :20 milliamperes. An electric pickup furnishes on the average an alternating voltage of 0.8 volt. In order that with such an input potential the above output power may be secured there is needed at least a two-stage amplifier when using amplifying tubes of the kind nowadays customary. A similar situation prevails for broadcast reception. Even if local reception is to be satisfactory where the alternating potential at the audion grid is approximately one volt, a two-stage set is necessary inasmuch as the loudspeaker tubes nowadays known demand a far higher grid potential for the modulation of :20 milliamperes, or, in other words, have far too small a slope.

Nevertheless, the advantages of an efficient one-stage receiver will be evident. Quite apart from the savings in cost attainable by dispensing with the second stage, also quality of reproduction is assured from the outset by the absence of any frequency-dependent coupling means. In

order that this end may be attained, what is employed according to this invention is a tube possessing a great slope, say, 20 milliamperes per volt and over. In order to realize such a slope there is particularly suited the kind of regulator cathode the nature of which shall be described in what follows, reference being made to the accompanying drawing.

It is a well known fact that the regulating power of a grid becomes so much greater, the

greater its proximity to the cathode. For purely constructional or technical reasons it is not feasible to mount the grid so closely to the heated cathode that the slope which has above been considered necessary is actually realizable. Now,

the so-called regulator cathode is predicated upon this idea of regulating the current density of electron emission in such a way that directly at the control grid an equi-potential surface being at zero potential will be produced which, so

far as the control grid. is concerned, plays the part of an electron-emissive cathode, and which therefore may be regarded as a Virtual cathode. The requisite distribution of the current may be secured by the separate regulation of the electron density and the electron Velocity.

This is accomplishable, e. g., by two grid shaped electrodes l, 2 which are interposed in tube 5 between the heated cathode 3 and the control grid 4, and on which fixed positive potentials are impressed. The inner grid 2 in such a scheme 10 serves for the dosing or volume-regulation of the emitted electrons, whereas the outer grid I serves to accelerate the same and control the velocity thereof. In order that the functions of these two grids may be made independent of each 15 other, a screen grid 6 may be inserted between the two. The electrode assembly comprising these grids and the heated cathode shall be here designated the regulator cathode. To realize such a regulator cathode one prime desideratum is a 20 uniform emission along the whole cathode, and it is on this ground that equi-potential cathodes of the indirectly heated kind are eminently suited for the present purpose.

The attached drawing shows a circuit scheme 25 comprising a tube of the regulator-cathode type, whence the function of the various grids will become clear. At the points marked TA an electric pick-up may be connected. In the circuit shown the lower side of tuning condenser 9 is 30 directly connected to cathode 3 while its upper side is connected to signal control grid 5 through the grid leak l and condenser 8. When signals of normal strength are received on the antenna, detection and amplification occur simultaneously 35 and the gain is sufficient to produce the requisite current change of :20 milliamperes through the speaker L.

What is claimed is:

Means for operating a loudspeaker directly 40 from a single amplifying stage, said single stage comprising a tube having an indirectly heated cathode, a heater element for said cathode, an anode, a signal control grid, a pair of grids interposed between said cathode and signal con- 45 trol grid, an input circuit connecting said signal control grid and cathode and including a portion tunable to the incoming signal frequency, means in said input circuit to cause rectification of the signal currents, a source of radio frequency 50 signal energy coupled to said tunable portion of the input circuit, means for'maintaining each grid of said pair at a substantially constant positive potential in the presence of Voltage Variations of said signal control grid due to currents in said input circuit, the inner grid of said pair being at a lower potential than the outer one and an output circuit connecting said anode and cathode and including said loudspeaker.

GUNTHER JOBST. DIETRICH PRINZ. 

